Radon Progeny Exposure and Lung Cancer: A Mortality Study of Newfoundland Fluorspar Miners 1950–2001 (RSP-0193)

Overview

Radon and radon decay products (RDP) also referred to as “radon progeny” emit types of radiation that are hazardous to people's health.

Radon is an odourless, colourless radioactive gas that occurs naturally in the environment as a result of the radioactive decay of uranium in soils and rocks. Radon decays through a series of very short-lived elements (polonium-218, lead-214, bismuth-214 and polonium-214) called radon decay products. RDP are not gases, but solid electrically charged particulates that will become suspended in the air, most attaching to dust particles or the surface of solid materials; some may remain unattached. Both attached and unattached fractions may be inhaled. If deposited in the lungs these decay products emit alpha radiation, and possibly damaging the living cells lining the lung.

While fluorspar miners were not nuclear energy workers, they represented a unique study opportunity. Their exposure was due to groundwater with high concentrations of natural radon that seeped into the mine and was released into the mine air. Because there were no other radiation exposures, it was possible to assess the risk from radon alone.

Learn more about radon.

Quick facts:
  • This study is an updated analysis of the mortality rate of a study group, or cohort, of Newfoundland fluorspar miners exposed to RDP.
  • This study concludes that:
    • Overall, miners were as healthy as the general Newfoundland male population.
    • The risk of lung cancer mortality was modified by the attained age, time since exposure, exposure rate and duration of RDP exposure.
    • The cohort was not large enough to determine the risk of developing different types of lung cancer.
    • The risk of lung cancer mortality was affected by cigarette smoking habits.
  1. Purpose of the study
  2. Background
  3. Methods
  4. Main results and conclusions
  5. Next steps
  6. Detailed study conclusions

Top of page


Purpose of the study

  • Understand the relationship between RDP exposure and lung cancer by examining lung cancer deaths (1950–2001) in workers who were exposed to RDP.

Background

  • Fluorspar is a non-metallic ore used in the manufacturing of aluminum and glass.
  • In the mid-1940s, an abnormally high number of fluorspar miners suffered from what was diagnosed as tuberculosis.
  • In the 1950s, a local physician observed an increased number of new lung cancer cases and alerted health officials to a possible cancer risk for the fluorspar miners.
  • In November 1959, it was discovered that the St. Lawrence fluorspar mine air contained radon gas in concentrations that vastly exceeded permissible levels of that time.
  • In 1960, mechanical ventilation systems were installed in the mines, and RDP exposures fell to well below the permissible standards of the time.
  • The above stated observations led to many studies of RDP-exposed groups looking at the relationship between RDP exposure and lung cancer mortality. The Newfoundland fluorspar miners have been extensively studied (DeVilliers et al 1964, Parsons et al 1964, DeVilliers et al 1971, Wright et al 1977, DeVilliers et al 1981, Morrison et al 1981, Morrison et al 1985, Morrison et al 1988, Corkhill et al 1984, Morrison et al 1995, Morrison et al 1998, Villneuve et al 1997, and Choi 1992).
  • The source of radiation in the fluorspar mines was from groundwater and not from radioactive ore. Therefore it was possible to exclude the effects of gamma radiation, thoron and radioactive dust from the risk estimates. This was not possible in other miner studies such as the Eldorado and Ontario uranium miners' studies.

Top of page

Methods

  • The cohort was constructed by using occupational records. Miners who lacked adequate identifying information (such as name, date of birth, etc.) were excluded from analysis.
  • Employees' radiation exposures were collected from 1950 to 2001. However, there is considerable uncertainty with the accuracy of the estimated RDP exposures before 1960.
  • The mortality (1950–2001) was determined by linking the miners' occupational records to the Canadian Mortality Database.
  • In 2003, a smoking survey was conducted to update previously collected data on the smoking habits of the fluorspar miner cohort. Previous smoking surveys of this group were conducted in 1966, 1970, 1978 and 1993.

Top of page

Main results and conclusions

  1. Overall, miners were as healthy as the general Newfoundland male population.
  2. The risk of lung cancer mortality was modified by the attained age, time since exposure, exposure rate and duration of RDP exposure.
  3. The cohort was not large enough to determine the risk of developing different types of lung cancer.
  4. The risk of lung cancer mortality was affected by cigarette smoking habits.

Read more on the study conclusions.

Top of page

Next steps

  • The post-1960 workers are still relatively young so most are not at the age when background lung cancer becomes a common cause of death.
  • Continued follow-up of these workers would be valuable; however, the statistical power may be limited because only 743 miners started working post-1960.

Return to main health studies web page.

To obtain a copy of the report (in English only), contact the CNSC.

 


Top of page


Detailed study conclusions

Conclusion 1: Overall, miners were as healthy as the general Newfoundland male population.

Supporting evidence:

  • For all causes of death, the mortality rate of the miner cohort was no different from the male Newfoundland population.
  • When considering each cause of death individually, the findings are consistent with previous analyses which show excess rates of cancer of the trachea, bronchus, and lung; silicosis; and accidents, poisoning and violence.
  • Reduced mortality rates of circulatory disease were observed in the cohort, which is likely due in part to a “healthy worker effect”.

Conclusion 2: The risk of lung cancer mortality was modified by the attained age, time since exposure, exposure rate and duration of RDP exposure.

Supporting evidence:

  • The risk of lung cancer mortality decreased with attained age (the risk was greater for those less than 50 years of age compared to those who were 70 years of age and older).
  • The risk of lung cancer mortality decreased with increasing time since RDP exposure.
  • The risk of lung cancer mortality decreased with increasing exposure rate.
  • The risk of lung cancer mortality increased with the duration of RDP exposure.

Conclusion 3: The study concluded that it would not be feasible to investigate the risk of excess lung cancer in modern miners because exposures are so low. It would also be practically impossible to accurately correct for the effects of smoking and residential radon, factors that could greatly impact the study results.

Supporting evidence:

  • Morphology information (type of lung cancer) was only available for 97 of the 206 lung cancer deaths.
  • Due to the small number of cases for each type of lung cancer, it was not possible to estimate the additional risk of developing one of the four types of lung cancer studied from the radiation exposures experienced in this cohort.

Conclusion 4: The risk of lung cancer mortality was affected by cigarette smoking habits.

Supporting evidence:

  • The risk of lung cancer mortality increased with increasing number of cigarettes smoked daily.
  • In 2003, smoking information was collected for 547 (26 percent) miners and 1,107 out of 2,059 miners have some smoking information.
  • Smoking behaviours have changed over time, with approximately 20 percent fewer smokers in 2003 than 1997.

Top of page

Additional information

  • All miners were male.
  • A total of 836 deaths from all causes were identified among the 1,742 underground miners, and 179 deaths from all causes were identified among 328 miners who worked exclusively on the surface. A total of 206 lung cancer deaths were observed in the cohort as a whole.
  • Tobacco smoking is the number one cause of lung cancer in Canada. It is responsible for 30 percent of all cancer deaths and is related to more than 85 percent of lung cancer cases in Canada. The risk for current smokers is approximately 20 times that of non-smokers.
  • Exposure to RDP is the second leading cause of lung cancer.
  • Thus, it is important to consider the potential impact of smoking on risk estimates when interpreting studies such as this.
  • Lung cancer is a known occupational hazard for underground miners with high exposures to RDP. High levels of exposures occurred during early mining operations when proper ventilation and radiation protection programs were not in place.
  • The findings in this study are consistent with the results of other miner studies and a combined analysis of the data from 11 underground miner studies (BEIR VI Report). They are also consistent with the conclusions of a recent report published by UNSCEAR (UNSCEAR, 2009) that provides a comprehensive review and summary of the sources and effects of radon in homes and workplaces.

To obtain a copy of the report (in English only), contact the CNSC.

 

Top of page

Related links

Top of page